mirror of
https://github.com/Fishwaldo/Star64_linux.git
synced 2025-03-16 12:14:06 +00:00
KVM: x86: Use current rather than snapshotted TSC frequency if it is constant
Don't snapshot tsc_khz into per-cpu cpu_tsc_khz if the host TSC is constant, in which case the actual TSC frequency will never change and thus capturing TSC during initialization is unnecessary, KVM can simply use tsc_khz. This value is snapshotted from kvm_timer_init->kvmclock_cpu_online->tsc_khz_changed(NULL) On CPUs with constant TSC, but not a hardware-specified TSC frequency, snapshotting cpu_tsc_khz and using that to set a VM's target TSC frequency can lead to VM to think its TSC frequency is not what it actually is if refining the TSC completes after KVM snapshots tsc_khz. The actual frequency never changes, only the kernel's calculation of what that frequency is changes. Ideally, KVM would not be able to race with TSC refinement, or would have a hook into tsc_refine_calibration_work() to get an alert when refinement is complete. Avoiding the race altogether isn't practical as refinement takes a relative eternity; it's deliberately put on a work queue outside of the normal boot sequence to avoid unnecessarily delaying boot. Adding a hook is doable, but somewhat gross due to KVM's ability to be built as a module. And if the TSC is constant, which is likely the case for every VMX/SVM-capable CPU produced in the last decade, the race can be hit if and only if userspace is able to create a VM before TSC refinement completes; refinement is slow, but not that slow. For now, punt on a proper fix, as not taking a snapshot can help some uses cases and not taking a snapshot is arguably correct irrespective of the race with refinement. Signed-off-by: Anton Romanov <romanton@google.com> Reviewed-by: Sean Christopherson <seanjc@google.com> Link: https://lore.kernel.org/r/20220608183525.1143682-1-romanton@google.com Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
parent
b80732fdc9
commit
3ebcbd2244
1 changed files with 33 additions and 11 deletions
|
@ -2974,6 +2974,22 @@ static void kvm_update_masterclock(struct kvm *kvm)
|
|||
kvm_end_pvclock_update(kvm);
|
||||
}
|
||||
|
||||
/*
|
||||
* Use the kernel's tsc_khz directly if the TSC is constant, otherwise use KVM's
|
||||
* per-CPU value (which may be zero if a CPU is going offline). Note, tsc_khz
|
||||
* can change during boot even if the TSC is constant, as it's possible for KVM
|
||||
* to be loaded before TSC calibration completes. Ideally, KVM would get a
|
||||
* notification when calibration completes, but practically speaking calibration
|
||||
* will complete before userspace is alive enough to create VMs.
|
||||
*/
|
||||
static unsigned long get_cpu_tsc_khz(void)
|
||||
{
|
||||
if (static_cpu_has(X86_FEATURE_CONSTANT_TSC))
|
||||
return tsc_khz;
|
||||
else
|
||||
return __this_cpu_read(cpu_tsc_khz);
|
||||
}
|
||||
|
||||
/* Called within read_seqcount_begin/retry for kvm->pvclock_sc. */
|
||||
static void __get_kvmclock(struct kvm *kvm, struct kvm_clock_data *data)
|
||||
{
|
||||
|
@ -2984,7 +3000,8 @@ static void __get_kvmclock(struct kvm *kvm, struct kvm_clock_data *data)
|
|||
get_cpu();
|
||||
|
||||
data->flags = 0;
|
||||
if (ka->use_master_clock && __this_cpu_read(cpu_tsc_khz)) {
|
||||
if (ka->use_master_clock &&
|
||||
(static_cpu_has(X86_FEATURE_CONSTANT_TSC) || __this_cpu_read(cpu_tsc_khz))) {
|
||||
#ifdef CONFIG_X86_64
|
||||
struct timespec64 ts;
|
||||
|
||||
|
@ -2998,7 +3015,7 @@ static void __get_kvmclock(struct kvm *kvm, struct kvm_clock_data *data)
|
|||
data->flags |= KVM_CLOCK_TSC_STABLE;
|
||||
hv_clock.tsc_timestamp = ka->master_cycle_now;
|
||||
hv_clock.system_time = ka->master_kernel_ns + ka->kvmclock_offset;
|
||||
kvm_get_time_scale(NSEC_PER_SEC, __this_cpu_read(cpu_tsc_khz) * 1000LL,
|
||||
kvm_get_time_scale(NSEC_PER_SEC, get_cpu_tsc_khz() * 1000LL,
|
||||
&hv_clock.tsc_shift,
|
||||
&hv_clock.tsc_to_system_mul);
|
||||
data->clock = __pvclock_read_cycles(&hv_clock, data->host_tsc);
|
||||
|
@ -3108,7 +3125,7 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
|
|||
|
||||
/* Keep irq disabled to prevent changes to the clock */
|
||||
local_irq_save(flags);
|
||||
tgt_tsc_khz = __this_cpu_read(cpu_tsc_khz);
|
||||
tgt_tsc_khz = get_cpu_tsc_khz();
|
||||
if (unlikely(tgt_tsc_khz == 0)) {
|
||||
local_irq_restore(flags);
|
||||
kvm_make_request(KVM_REQ_CLOCK_UPDATE, v);
|
||||
|
@ -9038,9 +9055,11 @@ static void tsc_khz_changed(void *data)
|
|||
struct cpufreq_freqs *freq = data;
|
||||
unsigned long khz = 0;
|
||||
|
||||
WARN_ON_ONCE(boot_cpu_has(X86_FEATURE_CONSTANT_TSC));
|
||||
|
||||
if (data)
|
||||
khz = freq->new;
|
||||
else if (!boot_cpu_has(X86_FEATURE_CONSTANT_TSC))
|
||||
else
|
||||
khz = cpufreq_quick_get(raw_smp_processor_id());
|
||||
if (!khz)
|
||||
khz = tsc_khz;
|
||||
|
@ -9061,8 +9080,10 @@ static void kvm_hyperv_tsc_notifier(void)
|
|||
hyperv_stop_tsc_emulation();
|
||||
|
||||
/* TSC frequency always matches when on Hyper-V */
|
||||
for_each_present_cpu(cpu)
|
||||
per_cpu(cpu_tsc_khz, cpu) = tsc_khz;
|
||||
if (!boot_cpu_has(X86_FEATURE_CONSTANT_TSC)) {
|
||||
for_each_present_cpu(cpu)
|
||||
per_cpu(cpu_tsc_khz, cpu) = tsc_khz;
|
||||
}
|
||||
kvm_caps.max_guest_tsc_khz = tsc_khz;
|
||||
|
||||
list_for_each_entry(kvm, &vm_list, vm_list) {
|
||||
|
@ -9199,10 +9220,10 @@ static void kvm_timer_init(void)
|
|||
}
|
||||
cpufreq_register_notifier(&kvmclock_cpufreq_notifier_block,
|
||||
CPUFREQ_TRANSITION_NOTIFIER);
|
||||
}
|
||||
|
||||
cpuhp_setup_state(CPUHP_AP_X86_KVM_CLK_ONLINE, "x86/kvm/clk:online",
|
||||
kvmclock_cpu_online, kvmclock_cpu_down_prep);
|
||||
cpuhp_setup_state(CPUHP_AP_X86_KVM_CLK_ONLINE, "x86/kvm/clk:online",
|
||||
kvmclock_cpu_online, kvmclock_cpu_down_prep);
|
||||
}
|
||||
}
|
||||
|
||||
#ifdef CONFIG_X86_64
|
||||
|
@ -9362,10 +9383,11 @@ void kvm_arch_exit(void)
|
|||
#endif
|
||||
kvm_lapic_exit();
|
||||
|
||||
if (!boot_cpu_has(X86_FEATURE_CONSTANT_TSC))
|
||||
if (!boot_cpu_has(X86_FEATURE_CONSTANT_TSC)) {
|
||||
cpufreq_unregister_notifier(&kvmclock_cpufreq_notifier_block,
|
||||
CPUFREQ_TRANSITION_NOTIFIER);
|
||||
cpuhp_remove_state_nocalls(CPUHP_AP_X86_KVM_CLK_ONLINE);
|
||||
cpuhp_remove_state_nocalls(CPUHP_AP_X86_KVM_CLK_ONLINE);
|
||||
}
|
||||
#ifdef CONFIG_X86_64
|
||||
pvclock_gtod_unregister_notifier(&pvclock_gtod_notifier);
|
||||
irq_work_sync(&pvclock_irq_work);
|
||||
|
|
Loading…
Add table
Reference in a new issue